The invention disclosed herein pertains generally to axial thrust bearings, and more particularly to axial thrust bearings which can absorb the axial thrust exerted on a rotating shaft of a turbomachine.
In the turbomachinery art, it is known to absorb the axial thrust exerted on a turbine shaft with a stationary, rigidly positioned thrust bearing which interacts with a shaft thrust plate. However, in order to maintain the thrust bearing in good operating condition, the peripheral speed of the shaft thrust plate should not exceed a certain value. That is, the variation of the magnitude of the axial thrust which can be absorbed by a single thrust bearing is narrowly circumscribed. On the other hand, it is often not possible, particularly in the case of gas turbines, to accurately predict the axial thrust occurring in operation. Thus, there is a relatively large uncertainty factor with respect to the load on the thrust bearing, especially in the case of large gas turbines having shafts of necessarily large diameter. Increasing the size of the thrust bearing, in order to take account of this uncertainty factor, is possible but only if the peripheral speed of the shaft thrust plate were to be increased beyond desirable limits.
The use of two thrust bearings would appear to be a solution to the problem described above. But the use of two rigidly positioned prior art thrust bearings, one arranged behind the other, is not possible because of longitudinal thermal expansions arising during operation, i.e. thermal expansions parallel to the shaft axis.
Accordingly, a primary object of the present invention is to provide a method and apparatus for precisely counterbalancing the axial thrust imparted to a shaft, even in the case of the very large diameter shafts of very large gas turbines.
A further object of the present invention is to provide a method and apparatus for counterbalancing the axial thrust imparted to a shaft, whereby the counterbalancing effect may be regulated according to the magnitude and direction of the axial thrust.
Yet a further object of the present invention is to provide a method and apparatus whereby two or more axial thrust bearings may be used to absorb and counterbalance the axial thrust imparted to a shaft.
Apparatus for absorbing and counterbalancing the axial thrust imparted to a shaft of a turbomachine, according to the present invention, includes at least two segmental thrust bearings arranged one behind the other in a stationary housing. The first thrust bearing includes bearing elements which are axially stationary and which interact with a first shaft thrust plate affixed to the shaft. The second thrust bearing includes bearing elements which interact with a second shaft thrust plate affixed to the shaft, and which bearing elements are axially movable relative to the first shaft thrust plate. A pressure tap from a compressor of the turbomachine leads to two regulatable throttle valves each of which is connected to a chamber or a line. Each of these chambers or lines has an outlet orifice leading to the atmosphere. The pressure in each of the chambers or lines is transmitted to bellows-like thrust chambers which interact with the bearing elements of the second thrust bearing to counteract the axial thrust imparted to the shaft.
A second embodiment of the present invention includes a compressor pressure tap leading to an oil filled reservoir. The oil pressure in a line emanating from the oil filled reservoir is regulated by a throttle valve. This oil pressure may be transmitted to one of two bellows-like thrust chambers through two additional oil lines. These bellows-like thrust chambers also interact with the movable bearing elements of a second thrust bearing arranged behind a first stationary thrust bearing.
The apparatus described above may be used for example to absorb the axial thrusts imparted to the shafts of water turbines, gas turbines, steam turbines or compressors.
The above apparatus is advantageous because the axial thrust acting on a shaft can be distributed over any desired number of thrust bearings. In addition, the load-carrying capacity of this apparatus increases as the load it must bear increases, i.e., as the rotational speed of the shaft increases.
The above apparatus is also advantageous because it permits a feedback controlled thrust compensation. That is, the thrust compensation increases as the pressure of the working medium increases, which pressure increases as the axial thrust increases.